1. Field of the Invention
The present invention relates to a working vehicle, and particularly relates to a working vehicle with a hydrostatic steering system.
2. Background Information
Working vehicles exist that travel as a result of power of an engine being transmitted to left and right propelling wheels by a first power transmission mechanism having a torque converter and transmission, etc. Such working vehicles with a hydrostatic steering system include a hydraulic oil pump driven by an engine, a hydraulic motor driven by pressurized oil from the hydraulic pump, and a second power transmission mechanism that transmits drive power of the hydraulic motor to the left and right drive wheels. The vehicle is then made to turn by making the speeds of the left and right drive wheels different using drive force of the hydraulic motor.
With this kind of hydrostatic steering system for a working vehicle, some of the output torque of the engine is used as absorption torque for the hydraulic pump in order to cause the vehicle to turn, and the remaining engine output torque is used as torque converter absorption torque for causing the vehicle to advance. It is therefore feared that the absorption torque of the torque converter will fall and that the traction performance will fall when the absorption torque of the hydraulic pump becomes larger as a result of increases in turning load. Further, there is the fear that engine speed will fall when the load on the engine becomes large.
With the hydrostatic steering system working vehicle of the related art, working vehicles exist where absorption torque of a hydraulic pump is controlled based on the speed ratio of the torque converter (refer to Japanese laid-Open Patent Application No. 2005-273902). The speed ratio of the torque converter is reduced or increased in accordance with increases in and falls in the traveling load. This working vehicle is therefore capable of controlling the absorption torque of the hydraulic pump in such a manner that turning performance is given priority when the traveling load is comparatively small. Further, it is possible to control the hydraulic pump absorption torque in such a manner that the required turning performance is ensured even when the traveling load is comparatively large.